The present invention relates to a planet carrier, and a method of making a planet carrier, and, more particularly, to a planet carrier in an epicyclic gear train comprising a central free cage ring having mounting holes which are axially parallel to the cage ring axis for receiving one end respectively of mounting pins; cage arm parts, each of which has a mounting hole which is axially parallel to the cage ring axis for receiving the other end respectively of the mounting pins; connection structure joined for movement with the cage arm parts, for connecting the planet carrier to a transmission member concentric to the cage ring axis; and connecting arms, disposed axially parallel to the cage ring axis, for connecting the free cage ring for movement with the cage arm parts joined to the connection structure, wherein the free cage ring and the connecting arms are formed as a one-piece sheet metal pressing.
Planet carriers of the type shown, for example, in Automobil-Industrie 4/79, p. 46, FIG. 13 are well known and are, in particular, used in motor vehicle automatic transmissions. In these known planet carriers, a basket-like planet carrier part, which is produced by stamping from a sheet blank followed by deep-drawing, and which consists of the cage ring and the connecting cage arms, is connected, generally by welding, to a flange part which combines not only the cage arm parts provided with the mounting holes but also the connection for the transmission part and may as desired be produced by stamping, forging or sintering.
DE 21 48 937 A1 also shows a planet carrier, in which, in contrast to planet carriers made of cast or pressed steel, the ends of the shafts of the planet gears are supported by holes which lie opposite one another. The holes are provided, on one hand, in a circular flange and, on the other hand, in the bottom, parallel thereto, of a cover whose peripheral part is welded to the periphery of the flange and which has cut-outs for the passage of the teeth of the planet gears. The flange and its cover are made of deep-drawn sheet metal.
DE 26 05 230 B1 discloses a different type planet carrier which is in one piece and consists of two side discs and a plurality of cage arms connecting the latter together. The planet carrier is provided with machined holes disposed entirely within the inside diameter of the cage arms and with axial stop faces which are raised in relation to the plane surface surrounding them and which completely surround the holes, for mounting the planet gears. In order to be able to manufacture this planet carrier, including its stop faces, at low cost, the stop faces are machined throughout, e.g. by turning, to a finished diameter smaller than the inside diameter of the cage arms and larger than the largest diameter of the stop faces in the region free from arms.
An object underlying the present invention consists essentially in reducing the cost of manufacture of a planet carrier. This object has been advantageously achieved by providing that the one-piece sheet metal pressing comprises not only the cage arm parts but also the edge portions thereof constituting the connection structure.
The planet carrier according to the present invention is brought into the desired shape, in its entirety and in one piece, by stamping a shaped flat sheet metal blank from a sheet blank and then folding it twice. On one side of the cage a stiff, closed cage ring is formed and on the opposite side individual lobes are formed, which can be welded either by their inner edge portions to a transmission shaft or by their outer edge portions to a drum-shaped part of a center gear, so that as a whole a stiff composite construction is once again obtained and transmission of the torque is made possible.